The present invention relates to magnetic storage devices and in particular to a magnetic storage device having a recording layer and an anchoring layer.
Magnetoresistive (MR) effect is a phenomenon that when a magnetic field is applied to a magnetic material, its electrical resistance varies and this phenomenon is utilized in magnetic field sensors, magnetic heads, and the like. As giant magnetoresistance (GMR) effect materials that exert especially profound magnetoresistance effect, artificial lattice films of Fe/Cr, Co/Cu, and the like are introduced in Non-patent Documents 1 and 2.
There is proposed a magnetoresistance effect element using a laminated structure of a ferromagnetic layer (free layer)/nonmagnetic layer/ferromagnetic layer (pin layer)/antiferromagnetic layer having a nonmagnetic metal layer thick to the extent that the exchange coupling action between the ferromagnetic layers is eliminated. In this element, the pin layer and the antiferromagnetic layer are exchange-coupled with each other and the magnetic moment of this ferromagnetic layer is fixed and only the spin of the free layer can be easily inverted by an external magnetic field. This is the element known as a so-called spin valve film. In this element, the exchange coupling between two ferromagnetic layers is weak and thus the spin of a free layer is inverted by a small magnetic field. For this reason, spin valve films can provide a magnetoresistive element having higher sensitivity than the above exchange coupling film can. As the antiferromagnetic material, FeMn, IrMn, PtMn, or the like is used. When this spin valve film is used, a current is passed in a film in-plane direction and it is used for reproducing heads for high-density magnetic recording because of the above-mentioned features.
A technology in which a laminated film of a ferromagnetic film/nonmagnetic film/ferromagnetic film is used for the above pin layer and the respective magnetizations of the two ferromagnetic films are coupled in antiparallel is disclosed, for example, in Patent Document 1. It is known that the influence of a pin layer on a free layer is smaller when this structure is used than when a single ferromagnetic film is used.
Non-patent Document 3 shows that the utilization of perpendicular magnetoresistance effect obtained by passing a current perpendicularly to a film surface makes it possible to obtain a profounder magnetoresistance effect.
In addition, Non-patent Document 4 shows tunneling magnetoresistive (TMR) effect arising from ferromagnetic tunnel junction. This tunnel magnetoresistance utilizes the following phenomenon in a three-layer film of a ferromagnetic layer/insulating layer/ferromagnetic layer: the magnitude of tunnel current perpendicular to a film surface is varied by making the spins of the two ferromagnetic layers parallel or antiparallel by an external magnetic field.
In recent years, for example, Non-patent Documents 5 to 7 describe researches on the utilization of GMR and TMR elements for nonvolatile magnetic storage semiconductor devices (MRAMs: Magnetic Random Access Memories).
In these cases, considerations have been given to pseudo-spin valve elements and ferromagnetic tunnel effect elements in which a nonmagnetic metal layer is sandwiched between two ferromagnetic layers different in coercive force. When such elements are utilized for MRAM, “1” and “0” are recorded by arranging these elements in a matrix pattern, passing a current through a separately provided wiring to apply a magnetic field, and controlling the two magnetic layers comprising each element into parallel and antiparallel. The GMR or TMR effect is utilized to read them.
In MRAMs, a power consumption is lower when the TMR effect is utilized than when the GMR effect is utilized; therefore, consideration is given to utilizing mainly TMR elements. In MRAMs utilizing TMR elements, the rate of MR change is as high as 20% or above at room temperature and the resistance in tunnel junctions is high; therefore, larger output voltage is obtained. In MRAMs utilizing TMR elements, further, it is unnecessary to invert spin in reading information and thus information can accordingly be read by a small current. For this reason, MRAMs utilizing TMR elements are expected as low-power consumption nonvolatile semiconductor storage devices capable of high-speed writing and reading.
In write operation with MRAMs, it is desired to control the magnetic characteristic of the ferromagnetic layers in each TMR element. Specifically, the following technologies are desired: a technology for controlling the relative direction of magnetization between two ferromagnetic layers sandwiching a nonmagnetic layer between them into parallel and antiparallel; and a technology for reliably and efficiently reversing the magnetization of one magnetic layer in a desired cell. For example, Patent Documents 2, 4, and 5 disclose technologies for uniformly controlling the relative direction of magnetization between two ferromagnetic layers sandwiching a nonmagnetic layer between them into parallel and antiparallel in a film surface using two crossing wirings.
In MRAMs, the following takes place when cells are miniaturized for higher degrees of integration: a reversed magnetic field is enlarged by a demagnetizing field depending on the size of a magnetic layer in the direction of its film surface. As a result, a large magnetic field is required when information is written and this increases power consumption as well. To cope with this, technologies for optimizing the shape of ferromagnetic layers and facilitating magnetization reversal have been proposed as disclosed in Patent Documents 3, 6, 7, and 8.    [Non-patent Document 1] D. H. Mosca et al., “Oscillatory interlayer coupling and giant magnetoresistance in Co/Cu multilayers,” Journal of Magnetism and Magnetic Materials 94 (1991) pp. L1-L5    [Non-patent Document 2] S. S. P. Parkin et al., “Oscillatory Magnetic Exchange Coupling through Thin Copper Layers,” Physical Review Letters, vol. 66, No. 16, 22 Apr. 1991, pp. 2152-2155    [Non-patent Document 3] W. P. Pratt et al., “Perpendicular Giant Magnetoresistances of Ag/Co Multilayers,” Physical Review Letters, vol. 66, No. 23, 10 Jun. 1991, pp. 3060-3063    [Non-patent Document 4] T. Miyazaki et al., “Giant magnetic tunneling effect in Fe/Al203/Fe junction,” Journal of Magnetism and Magnetic Materials 139 (1995), pp. L231-L234    [Non-patent Document 5] S. Tehrani et al., “High density submicron magnetoresistive random access memory (invited),” Journal of Applied Physics, vol. 85, No. 8, 15 Apr. 1999, pp. 5822-5827    [Non-patent Document 6] S. S. P. Parkin et al., “Exchange-biased magnetic tunnel junctions and application to nonvolatile magnetic random access memory (invited),” Journal of Applied Physics, vol. 85, No. 8, 15 Apr. 1999, pp. 5828-5833    [Non-patent Document 7] ISSCC 2001 Dig of Tech. Papers, p. 122    [Patent Document 1] Japanese Patent No. 2786601    [Patent Document 2] Japanese Unexamined Patent Publication No. Hei 11 (1999)-273337    [Patent Document 3] Japanese Unexamined Patent Publication No. 2002-280637    [Patent Document 4] Japanese Unexamined Patent Publication No. 2000-353791    [Patent Document 5] U.S. Pat. No. 6,005,800 Specification    [Patent Document 6] Japanese Unexamined Patent Publication No. 2004-296858    [Patent Document 7] U.S. Pat. No. 6,570,783 Specification    [Patent Document 8] Japanese Unexamined Patent Publication No. 2005-310971